1. Field of the Invention
The present invention relates to a semiconductor optical position sensing device for detecting the positions of optical beam projected on a semiconductor optical position sensing element.
2. Description of the Prior Art
An example of prior-art optical position sensing apparatus is disclosed in "Semiconductor Position Sensor and Its Application" ELECTRONIC MATERIAL, P119, Feb. 1980, as shown in FIG. 1.
In the drawing, an optical position sensing element 1 is formed with a flat and square-shaped light sensing plane of a pn junction of a high resistivity n-type Si, i.e., substrate 2 and a p-type layer 3. A first electrode 4 and a second electrode 5 are formed at an interval L near the two opposing side edges thereof. A first photoelectric current I.sub.1 can be detected through the first electrode 4 and a second photoelectric current I.sub.2 can be detected through the second electrode 5.
On the other hand, an n.sup.+ contact layer (not shown) is formed all over the outer surface of the Si substrate 2, and an electrode 6 is formed all over or on a portion of the n.sup.+ contact layer. A positive voltage +V.sub.CC is applied to the electrode 6 to reverse bias the pn junction of the sensing element.
A signal processing circuit as shown in FIG. 1 is connected to the optical position sensing element 1 to process the first and second photoelectric currents I.sub.1 and I.sub.2 detected through the first and second electrodes 4 and 5, respectively.
In more detail, the processing circuit comprises two current-voltage (C-V) converters 61 and 62, an adder 63, a subtracter 64, an inverter 65, a general purpose divider 66 and a DC-DC converter 67. The above C-V converters 61 and 62, adder 63, subtracter 64 and inverter 65 are all of the operational amplifier type. Further, the divider 66 is driven by voltages +V.sub.CC and -V.sub.EE supplied by the DC-DC converter 67.
In operation, when a light beam is projected on a position X (O .ltoreq..times..ltoreq.L) between the two electrodes 4 and 5 of the optical position sensing element 1, the first photoelectric current I.sub.1 detected through the first electrode 4 and the second photoelectric current I.sub.2 detected through the second electrode 5 both change relatively according to the optical position X as expressed below: EQU I.sub.1 =I.sub.0 .multidot.(L-X)/L (1) EQU I.sub.2 =I.sub.0 .multidot.X/L (2)
where I.sub.0 denotes the overall photoelectric current (I.sub.1 +I.sub.2) generated by the optical beam irradiation.
The first and second photoelectric currents I.sub.1 and I.sub.2 are converted into first and second voltages R.sub.f .multidot. I.sub.1 and R.sub.f .multidot. I.sub.2 by the current-voltage (C-V) converters 61 and 62, respectively. Both the voltages R.sub.f .multidot. I.sub.1 and R.sub.f .multidot. I.sub.2 are added by the adder 63 and inverted by the inverter 65 to obtain an addition voltage R.sub.f .multidot. (I.sub.1 +I.sub.2). On the other hand, both the voltages are subtracted by the subtracter 64 to obtain a subtraction voltage R.sub.f .multidot. (I.sub.2 -I.sub.1). The obtained subtraction voltage R.sub.f .multidot. (I.sub.2 -I.sub.1) is divided by the addition voltage R.sub.f .multidot. (I.sub.1 +I.sub.2) to obtain an output as follows: EQU (V.sub.ref /2).multidot.(I.sub.2 -I.sub.1)/(I.sub.1 +I.sub.2) =[(X/L)-1/2].multidot.V.sub.ref ( 3)
where V.sub.ref denotes a constant reference voltage.
The above expression (3) indicates that an optical position X can be detected by the divider 66 without being subjected to the influence of the quantity of optical beam irradiation.
In prior-art optical position sensing apparatuses as described above, since various circuit elements are required for the signal processing circuit, there exist various problems in that the number of parts is large; the size thereof is large; the cost is high; and, further, reliability is low.